Call selector



March 10, 1942. E. TORCHEUX CALL SELECTOR Filed March 9, 1939 INVENTOR 531% TORCHEUX BY- g ATTORNEY Patented Mar. 10, 1942 CALL SELECTOR Emile Torcheux, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Appiicatic-n March 9, 1939, Serial No. 260,762 In France March 11, 1938 6 Claims.

The invention relates to an electric circuit permitting the selection of signals of predetermined duration, i. e., whose duration extends between two given values.

Such a, device is useful in a great many cases, and more especially for providing a call selector.

The devices of this type hitherto produced have had the drawback that they were complicated and expensive. Moreover they very often required mechanical parts which were liable to get out of order.

The circuit according to the invention, on the contrary, is entirely electric and is adapted to actuate any suitable relay for controlling a bell or any such alarm apparatus as desired. The circuit is extremely simple and its operation is dependable.

This circuit is applicable in particular to the discriminatory reception of signals whose duration extends between very wide limits.

The principle of the circuit is as follows:

The received signals (received directly if they are direct current signals, or received following detection in the case of alternating current) act on a four-pole arrangement so constituted that inresponse to the arrival of these signals auxiliary impulsesare generated at the output terminals of the four-pole device. A resultant potential is then derived. from the combination of two opposing components, the one proportional to the signal and the other one whose value is as a function of time. and presents the pattern of a somewhat distorted sine wave.

Auxiliary impulses are also generated in response to the termination of the signals. Their value is a function. of time and they result from the combination of two opposing components, the one proportional to the signal which happens to cease, and the other one having a characteristic which will presently be explained.

There results from this double action a variation of the output potential which remains below a certain threshold value (release level) as long as there are no signals, or if signals arrive that are too short or too long.

However, a signal whose duration extends between certain limits generates at the moment of its cessation, a potential which surpasses the preceding threshold value and causes the actuation of any appropriate indicating means, such as an alarm signal, for instance.

The invention will be explained in a more explicit manner by reference to the accompanying drawing in which,

Figure 1 represents the scheme of a circuit in accordance with the invention;

Figs. 2a and 2b are graphic diagrams which are referred to in explaining the theory of operation of the invention; and

Figure 3 represents a particular application to radio signaling.

The operation of the system will be studied in detail in connection with the example illustrated in Fig. 1.

A signal as shown in Fig. 2a in the form of a continuous line of a certain duration t1 is, produces' a direct potential difference U at the input terminals AB of the circuit arrangement shown in Fig. 1. This circuit comprises two resistors R and R and two capacitors C and C. For the sake of simplicity the shunt resistance S across the terminals AB will be assumed to be somewhat low in comparison with the value of the series resistors R and R.

The control potential it of the circuit is applied to the indicating apparatus I across an electronic tube T Whose grid is negatively biased by a voltage U0 so as to provide a certain threshold of operation.

The output terminal I) of the circuit is connected to an intermediate point D of the resistance S. The potential drop in the part DB of this resistor causes a potential U1 to appear and this potential persists for the duration of the signal and is added algebraically to the potential U2 provided by the charge on the condensers C and C.

Fig. 2b shows a graphic plot on a time axis, of the output current u of the circuit.

In this figure the zero axis 0 of current values corresponds to the potential at the point D in Fig. 1.

If the signal beginning at the moment i1 is assumed to be a long dash, the potential U2 which then appears across the terminals of the resistor R. will have the pattern shown by the broken line curve g. The potential U2 which is zero up to the moment 151 when the signal starts increases up to a certain maximum m, after which it falls towards zero owing to the charge of the condensers C and 0. across the resistors R and R. In this way a quasi-harmonic curve will be obtained.

The potential U1 on the other hand, is proportional to U but has an opposite direction.

The resultant potential it will be the algebraic sum U2+U1 of the two preceding potentials. If the signal were to be prolonged without interhave the pattern of the curve 9.

Assume, however, that the signal terminates at the time t2. At this moment the potential U1 is annulled and the output potential u becomes equal to U2. The potential of the point a. will then pass from the point P to the point P and will operate the alarm apparatus if this point is above the level U of the operation threshold.

If then the curve 9 cuts the straight line u=Uo in two points M and M corresponding to the times t'z and t"z, it can be seen that the alarm device will function if the duration of the signal extends between the two values T1 (=t2-t1) and T2 (i"2-i1).

In order to bring these two values closer together, i. e., in order to render the apparatus more selective, it will be suiiicient to adjust the constants of the circuits and to control the potentials U1 and U2 with this object in view.

It should be well understood, however, that the above curves are entirely schematic and that they are given only for facilitating the explanation of the invention.

It is evident that in order to control independently. the time limits T1 and T2, the circuit shown in Fig. 1 can be replaced by a complex system comprising self inductances and capacitances.

The curves obtained in practice may also differ from those that have been shown, provided, however, that the curve U2=f(t) retains substantially the form indicated.

On the other hand, it should be understood that the invention may be carried out very usefully by a regulating device assuring, between certain limits, a correct functioning of the device despite the occurrence of variations in the amplitude of the received signals. It is quite evident in fact that the threshold of operation of the alarm device should principally depend only on the duration of the signals and not on their intensity or on the attenuation of their propagation.

Fig. 3 represents, by way of example, a preferred circuit arrangement for the low-frequency portion of a radio receiver, this being adapted to actuate an alarm device in accordance with the invention.

In this figure there is designated by the same letters the elements that have been shown already in Fig. 1. There is shown again the circuit having input terminals A, B, and output terminals a, b, the latter being disposed in the input circuit of a discharge tube T. An indicator or relay I is disposed in the output circuit of this tube.

The direct potential U which corresponds to the input signal as applied to the circuit is derived from a detector BF which feeds to a low frequency transformer Tr. Obviously the receiver would include the usual amplification stages, both for radio frequency and for intermediate frequency, also any device for changing the frequency and for detection purposes as well as any of the automatic volume control systems already known.

What I claim is:

1. Apparatus for discriminating in favor of a received impulse the duration of which is within predetermined limits, as against impulses of longer and shorter duration comprising a circuit having input terminals A and B and output terminals a and b, said input terminals being interconnected by three parallel circuits of which the first is constituted by a resistive potentiometer,

2,275,930 ruption, then the resultant potential 1/, would the second includes a resistor connected at one end to terminal A and a, capacitor connected between the other end of said resistor and terminal B, and the third includes said resistor, a second capacitor, and a second resistor, connected between the other end of said resistor and terminal A, a tap from an intermediate point on said potentiometer connected to said output terminal b, a connection from the junction between the second capacitor and the second resistor to output terminal a, and means including a discharge tube having a biased input circuit which includes said output terminals a and 1;, whereby a response to said received impulse is obtained only when the length of said impulse is within said predetermined limits.

2. A circuit arrangement having time constant elements adapted to discriminate between impulses of acceptable and inacceptable duration, said arrangement being constituted by three parallel circuit paths interconnecting input terminals A and B, the first of said paths being resistive and having an intermediate tap connected to an output terminal b, the second of said paths being resistive from terminal A and capacitive to terminal B, the third of said paths being resistive from terminal B and capacitive to the junction between the resistive and capacitive portions of the second path, an output terminal a connected to the junction between the resistive and capacitive portions of said third path, a discharge tube having cathode, anode and grid electrodes, the grid being connected to said output terminal a, and a grid biasing source interconnecting the cathode and said output terminal b.

3. A circuit arrangement of the class described, comprising input and output terminals, means including a potentiometer for deriving a substantially constant voltage component of a signal impressed on said input terminals during the time lapse of said signal, a time constant network connected across said input terminals and characterized in that it develops a, voltage component which first rises to a predetermined maximum and then falls as a function of a limited time interval following the initial application of said signal to said input terminals, an electron discharge tube having a biased input circuit which includes said output terminals, also a portion of said potentiometer and a conductive path in said time constant network, and means for impressing across said output terminals a resultant of said steady and variable voltage components combined in opposite sense, whereby said discharge tube is rendered conductive only upon termination of said signal within said limited time inter- Val.

l. A circuit arrangement according to claim 3 wherein said discharge tube is of the grid controlled gaseous type.

5. A circuit arrangement for delivering output impulses only in response to the reception of signal impulses having a duration between two predetermined limits, said arrangement comprising a potentiometer connected across a pair of input terminals, a series-connected resistor and capacitor in shunt with said potentiometer, a second series-connected resistor and capacitor in shunt with the first said capacitor, said second capacitor having one electrode connected to the junction between the resistor and capacitor first mentioned, and a discharge tube having input and output circuits, whereof the input circuit includes a portion of said potentiometer, the second mentioned resistor, and a grid biasing source, the two said series-connected resistors and capacitors constituting time-constant means for causing impulses of predetermined voltage to produce a conductive state in said discharge tube only when the duration of said impulses is between said two predetermined limits.

6. In a signaling circuit receptive of intermittent signals and adapted to be operated only by a signal impulse having a duration between two predetermined limits, a signal length measuring device comprising an electrical circuit having a characteristic such that a constant amplitude input voltage produces an output voltage first increasing as a function of the time, and then de- 15 creasing after passing through a predetermined maximum, means for applying to the input of said circuit a voltage responsive to signals, means for deriving the said output voltage by the superimposition on the input voltage of three auxiliary voltages, also responsive to signals, one of them of constant amplitude and of opposed sense to said input voltage, capacitors across which the two other of said voltages are developed as a function of time, one of them subtractively with a suitable retardation, and means for causing said signaling circuit to respond only to voltages exceeding a predetermined value and inferior to said maximum.

EMILE TORCHETJX. 

